Translocation ofMagnaporthe oryzaeEffectors into Rice Cells and Their Subsequent Cell-to-Cell Movement  

Abstract

Knowledge remains limited about how fungal pathogens that colonize living plant cells translocate effector proteins inside host cells to regulate cellular processes and neutralize defense responses. To cause the globally important rice blast disease, specialized invasive hyphae (IH) invade successive living rice (Oryza sativa) cells while enclosed in host-derived extrainvasive hyphal membrane. Using live-cell imaging, we identified a highly localized structure, the biotrophic interfacial complex (BIC), which accumulates fluorescently labeled effectors secreted by IH. In each newly entered rice cell, effectors were first secreted into BICs at the tips of the initially filamentous hyphae in the cell. These tip BICs were left behind beside the first-differentiated bulbous IH cells as the fungus continued to colonize the host cell. Fluorescence recovery after photobleaching experiments showed that the effector protein PWL2 (for prevents pathogenicity toward weeping lovegrass [Eragrostis curvula]) continued to accumulate in BICs after IH were growing elsewhere. PWL2 and BAS1 (for biotrophyassociated secreted protein 1), BIC-localized secreted proteins, were translocated into the rice cytoplasm. By contrast, BAS4, which uniformly outlines the IH, was not translocated into the host cytoplasm. Fluorescent PWL2 and BAS1 proteins that reached the rice cytoplasm moved into uninvaded neighbors, presumably preparing host cells before invasion. We report robust assays for elucidating the molecular mechanisms that underpin effector secretion into BICs, translocation to the rice cytoplasm, and cell-to-cell movement in rice.

LYM2-dependent chitin perception limits molecular flux via plasmodesmata

“…The PD protein PLASMODESMATA LOCATED PROTEIN 5 (PDLP5) was recently found to be required for resistance against Pseudomonas maculicola and to be associated with the deposition of callose at PD in this context (16). Also, in the interaction between rice cells and the blast fungus Magnaporthe oryzae, invasion hyphae seek out PD as sites to cross the cell wall (17), and the effector PWL2 moves from cell-to-cell ahead of the infection front (18). Thus, cellto-cell movement via PD appears to play a role in determining host susceptibility and pathogen virulence for nonviral biotic pathogens.…”

Multiple Rice MicroRNAs Are Involved in Immunity against the Blast Fungus Magnaporthe oryzae

“…The PTI-related genes, such as ent-Kaurene Synthase4 (OsKS4) and OsNAC4 (for Oryza sativa no apical meristem [NAM], Arabidopsis transcription activation factor [ATAF], and cup-shaped cotyledon [CUC] domain transcription factor4), can be induced by chitin in wild-type plants but suppressed in susceptible transgenic lines (Park et al, 2012). M. oryzae delivers a batch of effectors into rice cells through a biotrophic interfacial complex or invasive hyphae to enhance its virulence (Mosquera et al, 2009;Khang et al, 2010;Mentlak et al, 2012). Some effectors are recognized by intracellular receptors, termed R proteins, to trigger race-specific resistance that contributes to the postinvasive resistance.…”

A nuclear contortionist: the mitotic migration ofMagnaporthe oryzaenuclei during plant infection

“…Effectors function to dampen plant immune responses and change the metabolism of the plant (Giraldo et al 2013). The biotrophic interfacial complex (BIC) is a plant-derived membrane-rich structure that lies outside the fungal cytoplasm and is the site at which cytoplasmic effectors accumulate during plant infection (Khang et al 2010; Giraldo et al 2013). The BIC first appears at the tip of the primary hypha but then is repositioned to the side of the first bulbous cell (Khang et al 2010; Shipman et al 2017).…”

“…The biotrophic interfacial complex (BIC) is a plant-derived membrane-rich structure that lies outside the fungal cytoplasm and is the site at which cytoplasmic effectors accumulate during plant infection (Khang et al 2010; Giraldo et al 2013). The BIC first appears at the tip of the primary hypha but then is repositioned to the side of the first bulbous cell (Khang et al 2010; Shipman et al 2017). Cytoplasmic effectors are secreted to the BIC via non-conventional secretion and eventually enter plant cells, while apoplastic effectors undergo conventional secretion and remain contained within the extra-invasive hyphal membrane (Giraldo et al 2013).…”

“…The first-invaded rice cells are alive but die when the fungus enters adjacent cells (Kankanala et al 2007; Jones et al 2016b) Colonisation of the first-invaded plant cell takes approximately 8–12 h, while in subsequently invaded cells, the fungus only develops for 2–3 h (Kankanala et al 2007; Jones et al 2016b). One possible explanation for the difference in colonisation time between first-invaded and subsequently invaded cells is that effectors move cell-to-cell likely through plasmodesmata and prime neighbouring cells for fungal invasion (Kankanala et al 2007; Khang et al 2010). Within 4–5 days of initial infection, blast lesions become apparent on the plant tissue (Sakulkoo et al 2018).…”